Design Optimization of Single-Layer Antireflective Coating for GaAs P /Si Tandem C

Single-layer antireflective coating (SLARC) materials and design for GaAs P /Si tandem cells were analyzed by TCAD simulation. We have shown that optimum SLARC thickness is a function of bandgap, thickness, and material quality of top GaAs subcell. Cells are analyzed for P fractions , 0.17, 0.29, and 0.37, and ARC materials: Si₃N₄, SiO₂, ITO, HfO₂, and Al ₂O₃. Optimum ARC thickness ranges from 65–75 nm for Si₃N₄ and ITO to ∼100–110 nm for SiO₂. Optimum ARC thickness increases with increasing GaAs absorber layer thickness and with decreasing P fraction x. Simulations show that optimum GaAs absorber layer thickness is not a strong function of ARC material, but it increases from 250 nm for to ∼1 μm for and 0.37. For all P fractions, Si₃N₄, HfO₂, and Al₂O₃ performed almost equally, while SiO₂ and ITO resulted in ∼1% and ∼2% lower efficiency, respectively. Optimum SLARC thickness increases as the material quality of the top cell increases. The effect of ARC material decreases with decreasing GaAs material quality. The maximum efficiencies are achieved for cells with ∼1-μm GaAs_0.71 P_0.29 absorber ( ns): ∼26.57% for 75-nm Si₃N₄ SLARC and 27.62% for 75-nm SiO₂/60-nm Si₃N4 double-layer ARC.